Introduction to Microbiology Lecture 5 “Small creatures, big impacts” Lecture 5

Introduction to Microbiology Lecture outline Cell membranes, Spores, Motility Microbial reproduction- cell division and growth curves Bacterial conjugation and horizontal gene transfer Introduction to Microbiology

Cell membranes, spores, motility

Cytoplasmic (cell) membrane Thin structure that surrounds the cell 6–8 nm thick Vital barrier that separates cytoplasm from environment Highly selective permeable barrier; enables concentration of specific metabolites and excretion of waste products Cell membranes, spores, motility

Cytoplasmic (cell) membrane Phospholipid bilayer Hydrophobic and hydrophilic components Cell membranes, spores, motility

Cytoplasmic (cell) membrane Embedded proteins Mg2+ and Ca2+ stabilize (ionic bonds) Somewhat fluid Cell membranes, spores, motility

Cytoplasmic (cell) membrane Membrane-Strengthening Agents Sterols Rigid, planar lipids found in eukaryotic membranes Strengthen and stabilize membranes Hopanoids Structurally similar to sterols Present in membranes of many Bacteria Cell membranes, spores, motility

Cytoplasmic (cell) membrane Cell membranes, spores, motility Sterol (Cholesterol) Hopanoid (diploptene)

Cytoplasmic (cell) membrane Archaeal Membranes Ether linkages in phospholipids Bacteria and Eukarya: ester linkages Archaeal lipids: isoprenes instead of fatty acids Major lipids are glycerol diethers Can exist as lipid monolayers instead of bilayers Cell membranes, spores, motility

Cytoplasmic (cell) membrane Cell membranes, spores, motility Ester linkage Ether linkage Isoprene

Cytoplasmic (cell) membrane Cell membranes, spores, motility

Cytoplasmic (cell) membrane Cell membranes, spores, motility

Cell membranes, spores, motility Cytoplasmic membrane: major functions Cell membranes, spores, motility

Cell membranes, spores, motility Cell wall Provides support to cell Present in most Bacteria and Archaea Peptidoglycan in Bacteria Rigid layer that provides strength to cell wall Polysaccharide composed of N-acetylglucosamine and N-acetylmuramic acid Amino acids Cell membranes, spores, motility

Cell membranes, spores, motility

Cell membranes, spores, motility wall Peptidoglycan layer Plasma membrane Protein (a) Gram-positive: peptidoglycan traps crystal violet. Cell membranes, spores, motility

Cell membranes, spores, motility wall Peptidoglycan layer Plasma membrane Protein (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. Outer membrane Carbohydrate portion of lipopolysaccharide Cell membranes, spores, motility

Cell membranes, spores, motility Cell wall in Archaea No peptidoglycan Typically no outer membrane Some have Pseudomurein Polysaccharide similar to peptidoglycan Composed of N-acetylglucosamine and N-acetylalosaminuronic acid Other Archaea: Polysaccharide, glycoprotein or protein walls Cell membranes, spores, motility

Cell membranes, spores, motility

Attachment: Fibriae or Pilli Fimbriae 200 nm Cell membranes, spores, motility

Cell membranes, spores, motility Motility: Flagella Flagellum Filament Hook Basal apparatus Cell wall Plasma membrane 50 nm Cell membranes, spores, motility

Cell membranes, spores, motility Motility: Flagella Cell membranes, spores, motility

Cell membranes, spores, motility Chemotaxis Cell membranes, spores, motility

Cell membranes, spores, motility Endospores Highly differentiated cells resistant to heat, harsh chemicals, and radiation “Dormant” stage of bacterial life cycle Ideal for dispersal via wind, water, or animal gut Only present in some gram-positive bacteria Cell membranes, spores, motility

Cell membranes, spores, motility Endospores Cell membranes, spores, motility

Cell membranes, spores, motility Endospore survival Extremely long survival: 25-40 million years: Bacillus endospores trapped in the gut of an extinct bee preserved in amber > 250 million years: Halophile endospores trapped in salt crystals Cell membranes, spores, motility

Endospore survival: space travel? Life could have been delivered to Earth as part of a meteorite Bacillus spores can survive: Extreme acceleration Strong heating Survive radiation and dessication in deep space for nearly 6 years! Survive extreme pressure in simulated meteorite impacts Cell membranes, spores, motility

Prokaryote reproduction & conjugation

Bacterial fission: every 1-3 hours Microbial reproduction & conjugation

Considerable genetic variation Three factors: Rapid reproduction Mutation Genetic recombination Mutation rates: extremely low, e.g. 1 in 10 million cell divisions Rapid reproduction: e.g. 2 X 1010 new E. coli cells in human intestines per day Number of mutations per gene per day = (2X1010) (1X10-7) = 2000 Microbial reproduction & conjugation

Genetic recombination Three processes: transformation, transduction, and conjugation Important for Horizontal gene transfer Transformation: take up and incorporate foreign DNA from the environment Transduction: movement of genes between bacteria by bacteriophages Microbial reproduction & conjugation

Microbial reproduction & conjugation Recombinant cell Recipient cell A+ B– A– Recombination Donor B+ Phage DNA Microbial reproduction & conjugation

Microbial reproduction & conjugation Conjugation: genetic material is transferred between bacterial cells Sex pili allow cells to connect and pull together for DNA transfer F factor: Piece of DNA required for production of sex pili separate plasmid DNA within the bacterial chromosome Microbial reproduction & conjugation

Microbial reproduction & conjugation Sex pilus 1 µm Microbial reproduction & conjugation

Microbial reproduction & conjugation F Factor as plasmid: Cells containing F plasmid: DNA donors Cells without F factor: DNA recipients F factor transferable during conjugation Microbial reproduction & conjugation

Microbial reproduction & conjugation F Factor in chromosome: Cell with F factor built into chromosome: donor Recipient becomes recombinant bacterium, with DNA from two different cells HFR= High Frequency of Recombination Microbial reproduction & conjugation F factor Hfr cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome A+ A– F– cell Recombinant F– bacterium

Microbial reproduction & conjugation Gene transfer R plasmids: antibiotic resistance R plasmids carry genes for antibiotic resistance Antibiotics select for bacteria with genes that are resistant to the antibiotics Antibiotic resistant strains of bacteria are becoming more common Microbial reproduction & conjugation